cxx11-invoke

This is my attempt to use C++11 to implement std::invoke.

Introduction

We can use std::invoke to invoke callable objects (not just function objects). which additionally includes pointers to member function and pointers to data member.

Although std::invoke was added to the STL in C++17, we can still use STL facilities such as std::function or std::bind to call callable objects. All I did was just implement std::invoke using the language rules of C++11.

Usage

All APIs are implemented in the header file. You just need to add src/invoke.hpp to your project, and include it in the source file where you want to use it:

#include "invoke.hpp"	// You must use the correct path.

You can use it just like std::invoke. For example,

#include <string>
#include <iostream>
#include "invoke.hpp"

std::string s;
// invoke pointer to data member
std::cout << cxx11_invoke::invoke(&std::string::size, s);	

All the facilities you can use are listed below.

Library facilities

1. cxx11_invoke::invoke: invoke the callable object func with the parameters args.

   template<class Func, class... Args>
   constexpr typename cxx11_invoke::invoke_result<Func, Args...>::type
   invoke(Func&& func, Args&&... args) noexcept(...);

   Refer to the standard requirements of [std::invoke](std::invoke, std::invoke_r - cppreference.com) and [Callable](C++ named requirements: Callable - cppreference.com).

2. cxx11_invoke::invoke_result: Deduces the return type of an INVOKE expression at compile time.

   template<class Func, class... Args>
   struct invoke_result;

   Refer to the standard requirements of [std::invoke_result](std::result_of, std::invoke_result - cppreference.com).

3. cxx11_invoke::is_invocable: Determines whether Func can be invoked with the arguments Args....

   cxx11_invoke::is_invocable_r: Determines whether Func can be invoked with the arguments Args... to yield a result that is convertible to Ret.

   template<class Func, class... Args>
   struct is_invocable;
   
   template<class Ret, class Func, class... Args>
   struct is_invocable_r;

   Refer to the standard requirements of std::is_invocable and std::is_invocable_r.

About noexcept

Before C++17, noexcept is not a part of the function type. I didn't provide is_nothrow_invocable, because the type of the callable object does not contain noexcept information. But I still added the noexcept specifier to cxx11_invoke::invoke, which is just for completeness.